c++20 协程的运行步骤

#include <coroutine>
#include <iostream>
#include <thread>

namespace Coroutine {
  struct task {
    struct promise_type {
      promise_type() {
        std::cout << "1.create promie object\n";
      }
      task get_return_object() {
        std::cout << "2.create coroutine return object, and the coroutine is created now\n";
        return {std::coroutine_handle<task::promise_type>::from_promise(*this)};
      }
      std::suspend_never initial_suspend() {
        std::cout << "3.do you want to susupend the current coroutine?\n";
        std::cout << "4.don't suspend because return std::suspend_never, so continue to execute coroutine body\n";
        return {};
      }
      std::suspend_never final_suspend() noexcept {
        std::cout << "13.coroutine body finished, do you want to susupend the current coroutine?\n";
        std::cout << "14.don't suspend because return std::suspend_never, and the continue will be automatically destroyed, bye\n";
        return {};
      }
      void return_void() {
        std::cout << "12.coroutine don't return value, so return_void is called\n";
      }
      void unhandled_exception() {}
    };

    std::coroutine_handle<task::promise_type> handle_;
  };

  struct awaiter {
    bool await_ready() {
      std::cout << "6.do you want to suspend current coroutine?\n";
      std::cout << "7.yes, suspend becase awaiter.await_ready() return false\n";
      return false;
    }
    void await_suspend(
      std::coroutine_handle<task::promise_type> handle) {
      std::cout << "8.execute awaiter.await_suspend()\n";
      std::thread([handle]() mutable { handle(); }).detach();
      std::cout << "9.a new thread lauched, and will return back to caller\n";
    }
    void await_resume() {}
  };

  task test() {
    std::cout << "5.begin to execute coroutine body, the thread id=" << std::this_thread::get_id() << "\n";//#1
    co_await awaiter{};
    std::cout << "11.coroutine resumed, continue execcute coroutine body now, the thread id=" << std::this_thread::get_id() << "\n";//#3
  }
}// namespace Coroutine

int main() {
  Coroutine::test();
  std::cout << "10.come back to caller becuase of co_await awaiter\n";
  std::this_thread::sleep_for(std::chrono::seconds(1));

  return 0;
}